Residual NKT cells in SAP^−/−.BALB/c mice support NP-specific IgG response in the presence of Alum. (A) NKT cells of SAP^−/−.BALB/c mice were eliminated by crossing with Jα18^−/−.BALB/c mice. NKT cells in spleen and liver were identified with CD1d tetramer loaded with the αGalCer analog PBS57 and anti-TCRβ. (B) NP-specific serum IgG titers in SAP^−/−.BALB/c and SAP^−/−x Jα18^−/−.BALB/c mice 13 days after immunization with NP-KLH in alum. (C) The number of splenic GC B cells was determined by flow cytometry in mice immunized as in panel B.